1. Technical Field
The present invention relates to a method, an apparatus, and a program for assessing a degree of similarity or accuracy of a music performance on practicing relative to a model performance.
2. Background Art
Various types of musical instruments having a performance self-training function have been provided in the past. Keyboard instruments are taken for instance. This type of musical instrument having the self-training function directs a user to a key, which should be depressed, by means of display or the like on a display device, senses a key depressed by the user, informs the user of whether a correct key has been depressed, and prompts the user to train himself/herself a keyboard performance. For realization of the self-training function, a key depressed by a user has to be sensed. This poses a problem in that a keyboard instrument devoid of a key scan mechanism cannot be provided with the self-training function. Consequently, a proposal has been made of a technology for collecting a performance sound, analyzing the frequency of the sound, and deciding whether a performance sound having a correct pitch designated in a musical note has been generated, without need for sensing a manipulation performed on the keyboard or the like. For example, according to a technology disclosed in a patent document 1, various piano sounds of different pitches are collected, the frequencies of the sounds are analyzed, and a power spectrum of a piano sound of each pitch is obtained and stored in advance. When a piano performance is conducted, a performance sound is collected, and the frequency of the sound is analyzed in order to obtain a power spectrum. Similarities of the power spectrum of the performance sound to the power spectra of various piano sounds of different pitches that are stored in advance are obtained. Based on the degrees of similarities, a decision is made on whether the performance has been conducted accurately as prescribed in a music score.
[Patent Document 1] JP-A-2004-341026
[Patent Document 2] Japanese Patent No. 3413634
However, the power spectrum of an instrumental sound has generally an overtone component at many frequency positions. The ratio of overtone components is diverse. When there are two instrumental sounds to be compared with each other, although their fundamental frequencies are different from each other, the shapes of their power spectra may incidentally resemble. Therefore, the technology in the patent document 1 poses a problem in that when a performance sound of a certain fundamental frequency is collected, a piano sound whose fundamental frequency is different from the fundamental frequency of the performance sound but whose power spectrum resembles in shape with the power spectrum thereof may be selected, and the pitch of the performance sound may be incorrectly identified.